Technique that enhances oil recovery, sequesters CO2

New York Dec 20: A research team from the US has found a technique that not only increases oil recovery from wells but also sequesters more carbon dioxide in the process.

A research team from Pennsylvania State University proposed recovery technique for oil extraction that outperforms existing drilling and said the companies using this new technique could extract between 78 and 90 percent of the oil in a reservoir over several decades.

Existing drilling techniques in use today extract a maximum of 50 to 60 percent of the estimated total volume of oil before production, and on average, that number is closer to 35 percent.

Contrary to vertical drilling techniques, in which wells run perpendicular to the Earth's surface, the new technique uses horizontal drilling, in which wells are drilled up to about 4,000 metres, parallel to the Earth's surface, through known oil reservoirs.

The two wells, organised in a staggered line drive -- one well in the top of the reservoir to inject supercritical carbon dioxide into the system, and another well at the bottom of the reservoir to extract oil.

Carbon dioxide normally behaves like a gas at room temperature and pressure, but when it is pressurised and heated past a certain point -- the critical point -- it becomes a supercritical fluid, which exhibits liquid density and gas viscosity.

When injected at a continuous rate, supercritical carbon dioxide is an excellent solvent that is able to contact oil and form two hydrocarbon phases -- one that is light, containing a significant amount of carbon dioxide, and one that is denser, containing more oil.

"The idea of our model is that, if you can inject carbon dioxide as a supercritical fluid into the reservoir, it will extract light components from the oil, such as methane. This forms a less dense and less viscous fluid," said Russell Johns, professor of petroleum and natural gas engineering, Pennsylvania State University.

"Then, the reservoir is drained of water and oil, and the more buoyant, carbon-dioxide-rich fluid expands in a controlled way toward the lower well, where the oil can be extracted,"

The team used data from reservoirs in the Gulf of Mexico, and then developed a computerised simulation that ran 7,000 times to account for variations in reservoir properties that exist across the US.

Sequestering is the trapping of carbon dioxide in impermeable, non-porous layers of rock beneath the ground that prevent it from migrating upward.

The study was published in International Journal of Greenhouse Gas Control.